Golf clubs include a shaft and a head. The head generally includes a hosel, a face, a sole, and a back to form the hollow head. The face includes an exposed impact surface, upon which a golf ball impacts during a golfer's swing. The impact surface, though typically smooth over most of its surface area, can incorporate a number of different markings. These markings can be ornamental and provide no substantial effect on ball movement, or they can be designed to affect the movement of a ball striking the impact surface. The main factor in determining whether a marking on the impact surface affects ball movement is its depth. Decorative sandblasting or fine milling, for example, generally produces markings on the impact surface having depth less than about 0.10 mm. Though these markings are visible, they do not substantially affect the movement of a ball.
Other markings on the impact surface are designed to affect ball movement. For example, grooves commonly are used on the impact surfaces of club faces. The particular dimensions of these grooves are determined by the United States Golf Association (U.S.G.A.), as described in Appendix II of the U.S.G.A. Rules. These grooves generally range in depth from at least about 0.15 mm to about 0.50 mm (the maximum allowed under U.S.G.A. rules), and they are placed on the impact surface to provide increased spin rates for balls hit off the face. Increased spin rate provides increased aerodynamic lift and improved controllability of golf balls hit off the impact surface. Other markings, such as round punch marks, also can be used on the impact surface.
The ball markings discussed above designed to affect ball movement also can be aesthetically appealing. Golfers are accustomed to seeing grooves or other markings on the impact surfaces of club faces, and they generally do not prefer a “blank” look on a large portion of the impact surface. Besides their aesthetic appeal and effects on ball movement, markings on the impact surface serve as guides to golfers for proper placement the club prior to striking a ball. A golfer who is in an “address” position, in which he is preparing to hit a ball, looks down on the face at an angle generally parallel to the face. The golfer can use markings on the impact surface as landmarks, allowing for improved placement of his shot. Removing markings from the impact surface of the face removes this utility.
Despite the potential advantages above, use of deeper markings affecting ball movement, such as grooves, presents certain disadvantages. Because these markings cut more deeply into the impact surface of the face than the shallower decorative markings, the thickness of the face is substantially reduced at the markings. As a result, overall face thickness must be increased to maintain structural integrity of the face and prevent formation of stress fractures along the edges of the markings. This is particularly important for markings placed at the central region of the impact surface, because this region receives the greatest number of impacts, as well as impacts imparting the most force on the impact surface. Increasing the overall face thickness leads to a reduced coefficient of restitution (C.O.R.) for the club head, resulting in reduced ball speed and distance for balls hit using the head.
To prevent the need for thickening of the face, these deeper markings can be omitted from the impact surface, leaving only shallow decorative markings on the striking surface. This is particularly appropriate for driver heads that, as discussed above, do not require markings, such as grooves, to provide increased ball spin. However, use of these shallow markings alone provides for reduced utility of the markings, because they are difficult, if not impossible, to see at address when the golfer is viewing the impact surface at an angle generally parallel to the impact surface. The deeper markings are more clearly seen at address and provide superior guidance to a golfer.
In view of the above, there remains a need for a face for a golf club head that allows for high C.O.R. without formation of stress fractures on the impact surface of the face, while maintaining an appearance that is aesthetically appealing and serves as a guide to golfers. The present invention fulfills this need and provides related advantages.